1 John 5:16-17
If any man see his brother sin a sin which is not to death, he shall ask, and he shall give him life for them that sin not to death…
The leading thought which St. John had in his mind was not the distinction between different kinds of sin, but the efficacy of a Christian's prayers. He shows it to be an immediate consequence of our faith in Jesus Christ as the Son of God, that we should offer up our prayers in full confidence that those prayers will be heard, and that they will be answered, provided only that the petition is in accordance with God's holy will; and then he applies it to the question of intercession one for another; he would have us to remember, that if we have the privilege of coming to God's mercy seat, we ought not to use the privilege merely on our own behalf, but that we ought to pray for our brethren as well; and we may even pray for the forgiveness of their sins. But does this direction extend to all kinds of sins? Is there no limit to the power of intercession to obtain forgiveness of sin? St. John asserts that there is a limitation; he says that a Christian may obtain forgiveness for his brother by intercession, provided that the sin for which he prays has not been a deadly sin, a sin unto death. And though it may be very difficult to draw an exact line between the two kinds of sin of which the apostle speaks, yet we may sufficiently illustrate his meaning by taking two extreme cases. On the one hand, take the faults and failings which beset the very best amongst Christ's disciples; or again, taking the great question of steadfastness in the faith, which in St. John's day was a question of overwhelming importance to every Christian, one Christian might see his "brother sinning a sin not unto death" in this respect; then the faults of a weak brother such as this would be, as I conceive, a proper subject for the intercession of his brethren. But take the other extreme, suppose a man who has known what is right to have turned his back upon his convictions and to have wallowed in the filth of sin, or suppose you knew him to have committed any atrocious sin, would you have any reasonable ground to intercede for such a person at the throne of grace, and to expect to obtain forgiveness for him? Or suppose a person not merely to have shown some faltering and weakness concerning the faith, but to have openly and expressly denied the faith (which may have been the case that St. John had chiefly in his mind), then would a Christian have any right to ask for the forgiveness of this sin? It seems to me that in this case the very nature of the sin cuts off all possibility of intercession; for to intercede for pardon would be to plead those merits of Christ the virtue of which the apostate has himself expressly renounced.
(Bp. Harvey Goodwin.)
Parallel VersesKJV: If any man see his brother sin a sin which is not unto death, he shall ask, and he shall give him life for them that sin not unto death. There is a sin unto death: I do not say that he shall pray for it.
WEB: If anyone sees his brother sinning a sin not leading to death, he shall ask, and God will give him life for those who sin not leading to death. There is a sin leading to death. I don't say that he should make a request concerning this.